/Engine/Source/Runtime/GeometryCore/Public/Util/SmallListSet.h
Each list stores its count, so list-size operations are constant time. All the internal "pointers" are 32-bit.
class FSmallListSet
int32
AllocatedCount
Number of allocated lists
TDynamicVector<...
FreeBlocks
List of free blocks as indices/offsets into ListBlocks
int32
FreeHeadIndex
Index of first free element in linked_store
TDynamicVector<...
LinkedListElements
Flat buffer used to store linked-list "spill" elements each element is [value, next_ptr]
TDynamicVector<...
ListBlocks
Flat buffer used to store per-list linear-memory blocks.
TDynamicVector<...
ListHeads
Mapping from list index to offset into ListBlocks that contains list data